Conductor having axially-spaced wire helices and a helical wire terminal



Jan. 16, 1968 F. S. SLICK 3,364,302

CONDUCTOR HAVING AXIALLY5PACEU WINE HELLCES AND A HELICAL WIRE TERMINAL Filed Dec. 18, 1965 F7/6'@ l INVENTOR @En 5 2 /c/L United States Patent O 3 364,302 CONDUCTOR HAVING AXIALLY-SPACED WIRE HELICES AND A HELICAL WIRE TERMINAL Fred S. Slick, Rockford, Ill., assignor to Slick Electro Incorporated, Rockford, Ill., a corporation of Illinois Filed Dec. 18, 1963, Ser. No. 331,519 4 Claims. (Cl. 174-75) This invention relates to an electrical cable, and especially to the type of cable employed in aircraft ignition systems, and which cable has an outer metal shield to permit grounding the system. Presently-available stranded ignition cable frequently becomes accidentally shorted because the conductor kinks or buckles after the cable has been subjected to elevated temperatures, and then cools. The kinks or buckles short the system by causing the conductor to approach or actually make contact with the outer shield by parting the insulation. It is therefore an object of this invention to provide an electrical cable so constructed as to prevent such breakdown and shorting of the system.

Another object is to provide an electrical cable having a conductor that will not kink or buckle upon cooling.

Another object is to provide an electrical cable having a conductor that permits the convenient attachment of terminals thereto without requiring soldering.

Another object is to provide a cable of considerable flexibility, thus avoiding failure by crystallization caused by vibration.

Further objects and advantages of this invention will become` apparent from a consideration of the following detailed description taken in connection with the accompanying drawing wherein an embodiment of the invention is shown. It is, however to be understood that the invention is not to be limited to the details disclosed, but includes all such variations as fall within the spirit of the invention.

Referring to the drawing:

FIG. 1 shows a spark plug with which the present invention has been assembled.

FIG. 2 is a fragmentary view of the cable of this invention with portions of the insulation removed from the conductor.

FIG. 3 is a sectional View taken at 3 3 of FIG. 2.

FIG. 4 is a view of the spring terminal employed with the cable of FIG. 2.

FIG. 5 is an axial View of the terminal of FIG. 4.

FIG. 6 is an enlarged fragmentary view in section,y of a portion of FIG. 1, showing one method of mounting the terminal on the cable ofFIG. 2.

FIG. 7 is an enlarged fragmentary view of a portion of FIG. 6.

FIG. 8 shows another method of assembling the terminal of FIG. 4 with the cable of FIG. 2.

The cable 10 of this invention comprises a conductor 12 of metal Wire 14, preferably of stainless steel, and in this instance having a diameter of approximately 0.012 inch. Wire 14 is wound in the form of an open continuing cylindrical helix, in this instance having an axiallyexpanded pitch of approximately 0.040 inch, and of a major diameter of approximately 0.040 inch, and of the length desired.

Helical conductor 12 in this instance is first passed longitudinally through an extruding or similar process, and a cylindrical sheath 16 of silicone or similar resilient insulating material is applied, completely surrounding the wire 14. Sheath 16 is substantially larger in diameter than the major diameter of conductor 12, and completely surrounds Wire 14 as shown in FIG. 2. A customary sheath of woven fiber glass or similar ma- 3,364,302 Patented Jan. 16, 1968 ice terial 18 may be next applied over sheath 16 and resists excessive stretching of the cable 10.

A second resilient silicone rubber sheath 20 may, in some instances, be applied over the woven sheath 18, and finally a grounding sheath or shield 22 of woven wire is added to serve `as the usual means of providing a negative or ground when required. It is Within the purview of this invention to omit sheaths 18 and 20, and shield 22 when a specific situation does not require them: For example, when merely the sheath 16 is required as insulation over the conductor 12. The invention, however, resides mainly in the provision of a novel conductor as described, and the novel terminal means shown. The type of cable shown in FIG. 2 is usually specified for aircraft ignition systems.

The method of assembling cable 10 with a spark plug 24 is conventional with the exception of some details which will be explained, such as preparing the end of the cable to receive the terminal 26.

A thimble 28 is conventional with spark plugs used with aircraft ignition systems and is made of insulating material such as silicone rubber or the like. Thimble 28 has an axial bore 29 therethrough of a size to receive sheath 20 of cable 10. A second bore 31 of a diameter corresponding to the diameter of conductor 12, provides support for the latter.

Shield 22 is to be grounded to the body of plug 24I and a portion thereof Will be removed from the cable 10 when the latter is being prepared for assembly with the plug 24. A portion of sheaths 16, 18 and 20 are also removed, so that when cable 10 is assembled in the thimble 28, the ends of the sheaths will be recessed inwardly in bore 29 as shown in FIGS. 6, 7 and 8, uncovering conductor 12 as shown, and terminating as at 30. The resilient insulating material comprising sheath 16 is also removed from within the bore of conductor 12 by drilling the material therefrom as at 33 shown in FIG. 6.

Terminal 26, shown in FIGS. 4 through 8 is formed of Wire 34 of suicient resiliency and comprises a number of helical coils 36 having a major diameter larger than the bore 31 of FIG. 6, being the small bore in thimble 28. A Iminor helical portion 38 integral with coils 36 are of a diameter corresponding to that of conductor 12. Portion 38 comprises a plurality of helices 41 generally corresponding to those of conductor 12, both being wound left-hand in this instance. The pitch p', however, of portion 38 in this instance is greater than the pitch p of conductor 12 by approximately 20%.

One method of assembling terminal 26 with conductor 12 is shown in FIGS. 6 and 7 by mean-s of a core plug 32 of Wire, of a diameter slightly larger than the bore diameter of conductor 12. Wire 32 is inserted in the bore of conductor 12 and drilled hole 33. Plug 32 provides rigidity for the conductor and also maintains axial alignment between the latter and the portion 38 of terminal 26 in a manner to be described.

Terminal 26 is assembled with conductor 12 by rst placing portion 38 of terminal 26 on plug 32 by a rotating, interthreading operation so that the helices of the terminal portion 38, namely coils 41, are threaded intermediate those of conductor 12. This rotation is continued until the rst coil 36 of terminal 26 abuts the surface 40 of thimble 28. The differential in the pitches p and p of conductor 12 and portion 38 respectively, assure positive contact between these components in an axial direction. Plug 32 also assures axial alignment of conductor 12 and portion 38 of terminal 26. Additional support is also gained by supporting plug 32 in bore 33. Thimble 28 with cable 10 and terminal 26 assembled therewith is then inserted in plug 24 as shown in FIG. I

until an end coil 36 of the terminal engages a contact member 39 of the plug 24. The axial length of the coil portion 36 should be such as to assure positive contact between the coil 36 and contact member 39, when an end coil 36 abuts the surface 40. Previous to assembling as above, a portion of shield 22 is removed from cable 10, but a sufficient amount should be provided to engage a metal ferrule 42 which surrounds the shield 22 and makes a positive Contact therewith. Ferrule 42 is then assembled with a cap nut 44 which is in turn threaded to the body of plug '24, thus securing cable 10 axially in plug 24 and assuring a positive electrical contact between terminal 26 and contact member 39.

An alternate means to that shown in FIGS. 6 and 7 for attaching terminal 26 to conductor 12 is shown in FIG. 8. In this instance cable 10 is again prepared in the manner shown in FIG. 2. A tubular sleeve 46 of an inner diameter slightly smaller than the major diameter of conductor 12 and of a suitable length, is assembled over the conductor. The bore 47 of thimble 28 being of a size to receive sleeve 46. Cable 10 is then assembled in thimble as mentioned before and terminal 26 is threadedly engaged with conductor 12 within sleeve 46 by rotating the terminal relative to conductor 12. Conductor 12 and portion 38 of terminal 26 will be resiliently secured together owing to the fact that sleeve 46 compresses the conductor 12 and terminal portion 38 slightly. The cable 10 with thimble 28 and terminal 26 can then be assembled into plug 24 in the manner explained with respect to the assembly shown in FIGS. 6 and 7.

While this invention has been described as being assembled with a spark plug 24, it is to be understood that it can be employed in making similar connections with other components, such as magnetos, coils and such equipment.

It will be clear from the above description that this invention provides an improved cable that will not short by kinking or buckling during cooling after having been subjected to elevated temperatures such as those prevailing in aircraft power plant-s. The conductor of this invention will expand and contract axially in response to temperature changes; the changes merely resulting in lengthening or shortening of pitch p.

The above being a complete description of an illustrative embodiment of the invention, what is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A terminal means, for a conductor, said conductor having cylindrical axially-spaced wire helices, said terminal means comprising a minor cylindrical wire portion of a diameter corresponding to that of said helices and interthreaded therewith, and a major helical portion integral with said minor, co-axial therewith and of a diameter in excess of said minor portion.

2. A terminal means for a conductor, as set forth in claim 1, wherein said minor cylindrical helical wire portion has a pitch in excess of that of the helices of said conductor.

3. A terminal means for a conductor, said conductor having cylindrical, axially-spaced wire helices defining an axial bore therethrough, said terminal means comprising, in combination a wire helical cylindrical portion having an axial bore corresponding to that of said conductor, said helical portion being inter-threaded with said helices, and a cylindrical plug in said bore extending axially, and in common with said helices and said helical portion.

4. A terminal means for a conductor, said conductor having cylindrical, axially-spaced wire helices, said terminal means comprising, in combination a cylindrical helical wire portion having a diameter corresponding to that of said helices, a tubular sleeve surrounding said conductor at the extremity thereof, said helical wire portion being interthreaded with said helices and within said tubular sleeve.

References Cited LARAMIE E. ASKIN, Primary Examiner.

vJOHN F. BURNS, D. L. CLAY, ROBERT K.

SCHAEFER, LEWIS H. MYERS, Examiners.

D. A. KETTLESTRINGS, H. HUBERFELD,

Assistant Examiners. 

1. A TERMINAL MEANS, FOR A CONDUCTOR, SAID CONDUCTOR HAVING CYLINDRICAL AXIALLY-SPACED WIRE HELICES, SAID TERMINAL MEANS COMPRISING A MINOR CYLINDRICAL WIRE PORTION OF A DIAMETER CORRESPONDING TO THAT OF SAID HELICES AND INTERTHREADED THEREWITH, AND A MAJOR HELICAL PORTION INTEGRAL WITH SAID MINOR, CO-AXIAL THEREWITH AND OF A DIAMETER IN EXCESS OF SAID MINOR PORTION. 